402 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



gressed that Robertson, the French physicist, succeeded in reaching 

 an altitude of 22,000 feet, where he experienced an overpowering 

 sense of indifference. "There," said he, "the scientist is no longer 

 sensitive to the glory and passion of discoveries, and it is only by the 

 aid of a little fortifying wine that he succeeds in finding intervals of 

 mental clarity and power." 



Driven by the urge for greater range of action, man's ingenuity 

 devised means for ascent to ever higher altitudes, until in 1862 

 Glaisher, the English meteorologist, and Coxwell, his ballon engineer, 

 reached the limits of human survival. They went to a reported alti- 

 tude of 29,000 feet, but Glaisher was unconscious, and both would have 

 perished had not Coxwell, paralyzed though he was, seized the valve 

 cord in his teeth and released the gas by vigorously nodding his head. 

 On recovering consciousness, Glaisher voiced man's faith in the power 

 of science to break the bounds of human limitations: "I certainly 

 shall not take it upon myself," said he, "to set the limits of human 

 activity and indicate the point, if it exists, where nature tells the 

 aeronaut : 'You shall go no further.' " 



His confidence was soon justified, for it was but a few years later 

 that Paul Bert, the physiologist, discovered the cause of man's failure 

 at high altitudes and prescribed the means for overcoming this restric- 

 tion on human flight. Two causes were suspected : the reduced baro- 

 metric pressure and the lower volume concentration of oxygen in the 

 atmosphere. Both of these factors are now known to be a hazard 

 to the airman, but the cerebral symptoms then described were shown 

 by Bert to be the consequence of too little oxygen in the inspired air. 

 This he proved by placing a man in a large metal chamber, in which 

 he could be subjected to one or the other of the two conditions. 



From that time on, the vital dependence of the brain upon an ade- 

 quate and continuous supply of oxygen has been well recognized. The 

 recent development by my colleagues — Davies and Brink — of an elec- 

 trochemical method for measuring the concentration of oxygen among 

 the nerve cells of the intact cerebral cortex emphasizes this essential 

 need. By exact measurements, it is now possible to gain a clearer un- 

 derstanding of the brain's requirement for oxygen and the factors 

 which regulate the supply of this essential element. Pertinent to this 

 discussion is our observation that as the recording electrode is moved 

 to points on the cortex farther and farther from a blood vessel, the 

 concentration of available oxygen decreases steeply until, at a point 

 25-50 microns from a vessel, the concentration may be less than a 

 tenth of that in the arterial blood. This steep gradient of concentra- 

 tion insures effective diffusion of oxygen to the cells, but their avid 

 consumption keeps the reserve supply at a low level. In consequence 

 of this, a deficiency of oxygen in the blood is quickly followed by a 



